1. Field of the Invention
Aspects of the present invention relate generally to an image forming apparatus including a video controller improved to prevent emission of electromagnetic waves from being generated in processes of generating video data in synchronization with a video clock and a method of controlling the same.
2. Description of the Related Art
An image forming apparatus, such as a laser printer and a multifunction printer, includes a video controller that converts print data into video data and provides the video data to an exposing unit. An electrostatic latent image is formed in a photosensitive drum by the exposing unit. Toner is supplied to transfer a developed toner image to a sheet supplied by one from a sheet cassette so that the image can be printed onto a printable medium.
As shown in FIG. 1, the image forming apparatus includes a data processing unit 40 connected to a personal computer (PC) 10, a scanner 20, and/or a facsimile 30 to separately receive print data from the PC 10, the scanner 20, and/or the facsimile 30.
The data processing unit 40 processes the print data received from one of the PC 10, the scanner 20, and the facsimile 30 so that a video controller 50 processes the print data. The video controller 50 generates video data VDO with a reference clock and the print data received from the data processing unit 40 to transmit the video data VDO to an exposing unit 60. The exposing unit 60 provides the video data VDO received through a signal cable to a laser diode (not shown).
The video data VDO turns on or off the laser diode and controls the operation of the laser diode so as to form a part of the exposing unit 60 to which the toner is adhered and a part to which the toner is not adhered to correspond to a printed output image. The video controller 50 changes the duty ratio of the video data VDO using an algorithm for converting data to improve image quality and outputs the video data VDO.
The video data VDO, as shown in FIG. 2C, is generated using a video clock VCLK, shown in FIG. 2A, and a horizontal synchronizing signal Hsync, shown in FIG. 2B, that is a basis of scan lines. The video data VDO is toggled or clocked like the video clock VCLK so that electromagnetic interference is generated.
When a first pulse Vf1 and a second pulse Vf2 of the video data VDO are analyzed in a frequency domain, as shown in FIG. 3, a frequency spectrum Vf1 for the first pulse is distributed in a low frequency band and a frequency spectrum Vf2 for the second pulse is distributed in a relatively high frequency band. Since all of the frequency spectrums deviate from a reference value Es for electromagnetic interference determined by an international authority, the safety standard of a product is not satisfied.
According to a conventional method of improving the problems caused by the electromagnetic interference, a spread spectrum clock generator (SSCG) is used. The frequency of the reference clock varies in a predetermined range and the reference clock is provided to prevent an output signal from being similarly generated in the reference clock. The frequency of the reference clock is not fixed but varies so as to prevent the emission of electromagnetic waves.
When the SSCG is applied in order to solve the problems caused by the emission of the electromagnetic waves during the generation of the video data VDO, the frequency of the video clock VCLK must vary. In this case, the video data VDO is not generated normally. Therefore, a process of varying the frequency of the video clock VCLK in a very limited range is used. However, it is difficult to effectively prevent the electromagnetic interference due to the limited range.